Hackett was given a fine of £400 and Whalley a fine of £500. Both were ordered to pay £400 costs.

The pair were working on behalf of Blackhorse Finance Limited. Another private investigator subcontracted Whalley to track down a woman whose partner owed money. The ICO said today that Blackhorse believed any information would be obtained legally. But it wasn't.

Whalley passed the case to Hackett, who rang BT and convinced the operator he was a fellow employee. He was given the woman's home address which led to Blackhorse debt collectors paying her a visit.

Assistant Information Commissioner Mike Gorrill said in a statement: "Illegally obtaining and selling personal information is a serious offence which can be highly damaging to the individuals concerned. This prosecution is the result of a thorough investigation by the Information Commissioner’s Office and is part of our ongoing work to stop the illegal trade in personal information."

It's not known how much Hackett and Whalley were paid for their service. ®